Partial discharge detection test link, partial discharge detection system and methods for detecting partial discharge on a power cable

ABSTRACT

A partial discharge detection test link and system is disclosed to detect partial discharge of a power cable accessory. The power cable accessory includes a first accessory component and a second accessory component connected to each other. The partial discharge detection test link is a permanent or temporary substitute for a conventional service link, connects directly across the power cable accessory and includes a conductor member and a partial discharge sensor. The conductor member has an electrically conductive element and an insulation surrounding and extending along the electrically conductive element. The electrically conductive element is electrically connected directly between the first and second accessory components. The partial discharge sensor is disposed about the conductor member and has the electrically conductive element as a primary winding and a secondary winding with the insulation positioned between the primary and secondary windings.

This is a division of application Ser. No. 10/169,808, filed Mar. 17,2003, now U.S. Pat. No. 6,930,491 which claims priority toPCT/GB01/00321, filed Jan. 26, 2001, and further claims priority toUnited Kingdom Application No. 0001923.2, filed Jan. 27, 2000, all ofwhich are incorporated herein by reference.

BACKGROUND

The invention relates to apparatuses and methods for detecting partialdischarge on a power cable. The apparatuses and the methods areparticularly useful for detecting partial discharge on installedhigh-voltage power cables. More particularly, the apparatuses relate toa partial discharge detection test link and a partial dischargedetection system.

For satisfactory long-term performance extruded dielectric power cablesystems at stress levels used in modern extra-high-voltage cross-linkedpolyethylene (XLPE) cable systems, it is necessary to maintain highpurity levels of material and precision of manufacture. If not, one ormore latent defects may occur within the dielectric. For qualityassurance, the cables themselves as well as the accessory components arerigorously tested electrically prior to installation. However, defectscan subsequently be introduced. Such defects include external damage tocables or contamination thereof as well as mishandling or misalignmentof accessory components, particularly during installation.

Latent defects of this type can be detected by conducting a postinstallation electrical test. One such test, considered most sensitiveand revealing, measures partial discharge (PD) of the field-installedaccessories. This test energizes the power cable system with alternatingvoltage, at or near power frequency, and at a working voltage or a smallovervoltage.

It is impractical to conduct this test for long length of high voltagepower cable using a portable test voltage source. As a result, tests oninstalled power cable circuits are often conducted by connecting thecircuit to be tested to the electrical power cable system and monitoringits performance for a period of time. Upon satisfactory completion ofthe monitoring period, the circuit is then placed into commercialservice.

Power cable systems are sometimes installed without built-in PDmeasurement sensors in the accessories. If a PD measurement test is tobe conducted on such a circuit, it is necessary to provide PDmeasurement sensors for sensing PD signals. Usually, the PD measurementsensors are releasably connected to the service links. With reference toFIG. 1, a partial discharge sensor 2 is releasably disposed about aservice link 4. The service link 4 is attached to an accessory 6 in aform of a termination. The accessory 6 includes a first accessorycomponent 8, a second accessory component 10 and a sleeve 12 whichconnects the first accessory component 8 and the second accessorycomponent 10 to each other. Each of the first and second accessorycomponents 8 and 10 has a lug 14. Opposing ends of the service link 4are respectively connected to the lugs 14 by fasteners 15 such as screwsor bolts. By way of example only, the first accessory component 8 isconnected to switchgear 16 while a high-voltage cable 18 is connected tothe second accessory component 10.

The service link 4 is required to be added to the accessory when thepower cable system is in service in order to control voltages occurringon the power cable sheath by allowing flow of induced power frequencyand transient currents. The service link 4 can be fitted in a variety ofconfigurations to control the magnitude of the flowing current. Asillustrated in FIG. 1, the service link 4 is fitted directly to theaccessory 6. Also, service links can be used at remote enclosures, suchas link boxes or link kiosks, which are normally located with in a fewmeters of the accessories.

Many hazards are associated with energized power cable systems. Onehazard is standing power frequency voltages that exist between servicelinks and from service links to earth which arises from normal operationof the power cable system. Another hazard is transient voltages thatexist between service links and from service links to earth which arisesfrom switching operations, lightning strikes and the like. Yet anotherhazard is severe electrical arcing as a result of flashover involvingthe service links. Thus, there are three major considerations of safetyregarding testing of energized power cable systems. One, conductingpartial discharge tests on an energized power cable system should poseno risk of injury to living beings. Two, there should be no added risksof damage to the circuit being tested or equipment associated with thetests. Three, faults are likely to occur within the first few hours ofthe operation of the power cable system when PD testing is likely to bein progress.

SUMMARY

It is an object of the invention to provide a partial dischargedetection test link having built-in partial discharge sensor.

Another object of the invention is to provide a partial dischargedetection system and methods for minimizing risks of injury to livingbeings as well as risk of damage to the power cable circuit while beingtested.

Yet another object of the invention is to provide a partial dischargedetection system and methods that electrically isolate the circuit beingtested and measuring instruments.

Still yet another object of the invention is to provide a partialdischarge detection system and methods that do not require touching ofany electrical signal leads or other electrical connections while thecircuit is being tested.

Accordingly, a partial discharge detection test link of the invention, apartial discharge detection system and methods of the invention fordetecting partial discharge are hereinafter described. The partialdischarge detection test link of the invention detects partial dischargeof a power cable at a power cable accessory that includes a firstaccessory component and a second accessory component connected to eachother. The partial discharge detection test link of the inventionincludes a conductor and a partial discharge sensor. The conductormember includes an electrically conductive element and an insulationsurrounding and extending along the electrically conductive element. Theelectrically conductive element has a pair of opposite ends. Arespective one of the ends is adapted for electrical connection to arespective one of the first and second accessory components. The partialdischarge sensor is disposed about the conductor member. The partialdischarge sensor has primary winding and a secondary winding with theinsulation positioned between the primary winding and the secondarywinding.

The partial discharge detection system includes the conductor member anda partial discharge sensor similar to the one described above. Thepartial discharge detection system of the invention also includes afirst converter device, a second converter device and a partialdischarge measuring instrument. The partial discharge sensor isoperative to detect partial discharge of the power cable as partialdischarge electrical signals. The first converter device, electricallyconnected to partial discharge sensor, is operative for receiving thepartial discharge electrical signals from the partial discharge sensorand converting the partial discharge electrical signals to alternativeenergy signals representative of the partial discharge electricalsignals. The second converter device in communication with the firstconverter device is operative for receiving the alternative energysignals and converting the alternate alternative energy signals toelectrical output signals representative of the alternative energysignals. The partial discharge measuring instrument which is coupled tothe second converter device is operative to read the electrical outputsignals and measure the partial discharge from the power cable.

One method of the invention detects partial discharge on an energizedpower cable. The method of the invention includes the steps of detectingpartial discharge of the energized power cable at or adjacent to theenergized power cable by generating partial discharge electrical signalsrepresentative of the detective partial discharge; converting thepartial discharge electrical signals to alternative energy signalsrepresentative of the partial discharge electrical signals adjacent tothe power cable; transmitting the alternative energy signals to alocation remote from the energized power cable; and, interpreting thealternative energy signals in a manner to measure the partial dischargeof the energized power cable.

Another method detects partial discharge on the energized power cable.The method includes the steps of connecting the first accessorycomponent and the second accessory component together using the testlink; detecting the partial discharge of the energized power cable atthe test link by generating partial discharge electrical signals; and,interpreting the partial discharge electrical signals in a manner tomeasure the partial discharge of the energized power cable.

Yet another method of the invention detects partial discharge on aplurality of energized power cables positioned in an enclosure definedby an arrangement of walls. The method includes the steps of connectingrespected ones of the first accessory components and the secondaccessory components to each other using a plurality of electricallyinsulative connectors; directly electrically connecting the respectiveones of the first accessory components and the second accessorycomponents to each other using respective ones of the plurality of testlinks; positioning electrically insulative barriers between juxtaposedones of the plurality of energized cables to inhibit flashover;detecting partial discharge of the plurality of energized power cablesat respective test links by generating partial discharge electricalsignals; converting the partial discharge electrical signals adjacentthe enclosure to alternative energy signals; transmitting thealternative energy signals to a location remote from the enclosure; and,interpreting the alternative energy signals at the remote location in amanner to measure the partial discharge of the respective energizedpower cables.

Other objects and advantages of the invention will become apparent fromthe following description of the embodiments of the invention taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of an exemplary accessory having afirst accessory component and a second accessory componentinterconnected by a conventional service link with a conventionalpartial discharge sensor partially disposed about the service link;

FIG. 2 is a side elevational view of a first embodiment of a partialdischarge detection test link of the invention connected to theexemplary accessory;

FIG. 3 is a side elevational view of the partial discharge detectiontest link of the invention;

FIG. 4 is an enlarged elevational view in cross-section of the partialdischarge detection test link taken along line 4—4 in FIG. 3;

FIG. 5 is a side elevational view of a second embodiment of the partialdischarge detection test link of the invention that includes a currenttransformer;

FIG. 6 is a diagrammatical view of a partial discharge detection systemof the invention;

FIG. 7 is a perspective view of a plurality of partial dischargedetection test links with each connected to an alternative exemplaryaccessory disposed in a link box;

FIG. 8 is a perspective view illustrating a partial arrangement of thepartial discharge detection system disposed above the link box in FIG.7; and,

FIG. 9 is flowchart of a method for detecting partial discharge on anenergized power cable.

DESCRIPTION OF THE EMBODIMENTS

A partial discharge test link 20 of the invention is generallyintroduced in FIGS. 2–4. It is noted that identical elements designatedFIG. 1 are identified with the same referenced numerals in FIG. 2. Thepartial discharge detection test link 20 of the invention detectspartial discharge of the high voltage cable 18 at the power cableaccessory 6. As shown in FIG. 3, the partial discharge detection testlink 20 of the invention includes a conductor member 22 and a partialdischarge sensor 24. The conductor member 22 includes an electricallyconductive element 26 and an insulation 28 that surrounds and extendsalong the electrically conductive element 26. The electricallyconductive element 26 has a pair of opposite ends 30. As shown in FIG.2, a respective one of the ends 30 is adaptive for electrical connectionto a respective one of the first and second accessory components 8 and10 as is known in the art and illustrated in FIG. 1. As shown by way ofexample only, in FIG. 2, the power cable accessory 6 is a cabletermination, also known as a cable terminal. As illustrated in FIG. 2,the conductor member 22 is connected directly across the power cableaccessory 6. This direct connection, particularly for purposes oftesting the circuit, allows the freest flow of any possible faultcurrents through the partial discharge detection test link 20 of theinvention. Furthermore, this direct connection provides the optimumlowest-impedance path for power frequency and transient occurrenceflowing along the power cable.

With reference to FIGS. 2 and 3, the partial discharge detection testlink 20 of the invention also includes an electrically conductive cablelead 36 that extends from and is operably connected to the partialdischarge sensor 24. Although not by way of limitation, the cable lead36 has a cable terminal 38. Also, the partial discharge detection testlink 20 of the invention may also include a ground cable 40 that iselectrically connected to the electrically conductive element 26.

In FIG. 3, the pair of opposite ends 30 project from the insulation 28.An electrically conductive connector 42 in a form of an eyelet compriseseach opposite end 30. The electrically conductive connectors 42facilitate ease in fastening the partial discharge connection test link20 to the accessory 6 by the fasteners 15.

Preferably, the electrically conductive element 26 is fabricated from aflexible cable material such as copper wire. However, one of ordinaryskill in the art would appreciate that a rigid material that iselectrically conductive would also be suitable to practice theinvention. Preferably, the electrically conducted element 26 is abonding lead.

Although, not by way of limitation, the partial discharge sensor 24 is aradio frequency current transformer. The radio frequency currenttransformer can be either a ferrite-cored construction, an air-coredconstruction or a rogowski-coil construction. It is further preferredthat the partial discharge sensor 24 is an isolation-type radiofrequency current transformer. The radio frequency current transformeris operative to sense electromagnetic pulses emanating at a rapid ratefrom the energized power cable. The isolation type radio frequencycurrent transformer is optimized to yield high sensitivity to theelectromagnetic pulses emanating at this rapid rate. Simultaneously, theconductor member 22 is designed to tolerate substantial power frequencycurrents flowing through the electrically conductive element 26.

In FIG. 4, the secondary winding 34 of the partial discharge sensor 24is illustrated as being electrically isolated from the electricallyconductive element 26 by virtue of an insulation 28 being disposedtherebetween. The insulation 28 has a thickness “t” and the electricallyconductive element 26 has a diameter “d”. It is preferred that thethickness “t” of the insulation 28 is at least one half of the diameter“d” of the electrically conductive element 26.

An alternative embodiment of a partial discharge detection test link 120is depicted in FIG. 5. The partial discharge detection test link 120 ofthe invention includes identical elements of the partial dischargedetection test link described above. Additionally, the partial dischargedetection test link 120 includes a current transformer 44 which isdisposed about the conductor member 22. The current transformer 44 isoperative to sense power frequency flowing in the conductor member 22. Acurrent transformer lead 46 is electrically connected to the currenttransformer 44 at one end and includes a current transformer terminal 48at the opposite end.

A partial discharge detection system 50 of the invention is generallyintroduced in FIGS. 6–8. The partial discharge detection system 50includes the conductor member 22, the partial discharge sensor 24, afirst converter device 52, a second converter device 54 and a partialdischarge measuring instrument 56. The partial discharge sensor 24 isoperative to detect partial discharge of the energized power cable aspartial discharge electrical signals. The first converter device 52 iselectrically connected to the partial discharge sensor 24 as representedby line 58. The first converter device 52 is operative for receiving thepartial discharge electrical signals from the partial discharge sensor24. Also, the first converter device 52 is operative for converting thepartial discharge electrical signals to alternative energy signals whichare representative of the partial discharge electrical signals.

The second converter device 54 communicates with the first converterdevice 52 as represented by line 60. The second converter device 54 isoperative for receiving the alternative energy signals and convertingthe alternative energy signals to electrical output signalsrepresentative of the alternative energy signals. The partial dischargemeasuring instrument 56 is coupled to the second converter device 54 asrepresented by line 62. The partial discharge measuring instrument 56reads the electrical output signals and measures the partial dischargefrom the power cable 18.

Preferably, the alternative energy signals are optical signals. However,one of ordinary skill in the art would appreciate that the alternativeenergy signals can be radio frequency signals or other such signalscommonly used throughout the electromagnetic spectrum. If thealternative energy signals are optical signals, the first converterdevice 52 is preferably an optical encoding transmitter 52 a and thesecond converter device 54 is preferably an optical decoding receiver 54a. If the alternative energy signals are radio frequency signals, thefirst converter device 52 is preferably a radio frequency transmitter 52b and the second converter device 54 is preferably a radio frequencyreceiver 54 b.

As shown in FIG. 7, an alternative partial discharge detection test link120 is used thus providing the current transformer 44 for sensing powerfrequency current flowing in the conductor member 22 shown best in FIG.5. The current transformer 120 generates a power frequency currentsignal used in conjunction with the partial discharge measuringinstrument 56 for synchronizing the partial discharge measuringinstrument 56 with voltage frequency and voltage phase of a voltage inthe power cable when the power cable is energized.

With reference to FIGS. 7 and 8, the partial discharge detection testlink and the partial discharge detection system are illustrated by wayof example only. Note, in FIG. 7, the accessory 6 is in a form differentthan the one described above. By way of example, the accessory 6 is apair of bonding lead clamps with the first accessory component 8 beingone bonding lead clamp and the second accessory component 10 being aremaining one of the pair of bonding lead clamps. The pair of bondinglead clamps are connected together by a bonding lead 11. Thus, theinvention is adaptable to other types of accessories regardless of theirform and is not limited to the ones described herein.

A plurality of partial discharge detection test links 20 and 120 aredisposed in an enclosure 66 in a form of a buried link box. One ofordinary skill in the art would appreciate that an above-ground kiosk isanother example of the enclosure 66. Insulating barriers 68 areinstalled between the partial discharge detection test links within theenclosure 66 and between the partial discharge test links and walls 67of the enclosure 66 to reduce risks associated with flashover. Outputsfrom the plurality of the partial discharge sensors 24 and the currenttransformer 44 at each accessory position are connected to the opticalencoding transmitters 52 a shown in FIG. 8. The optical signals from theoptical encoding transmitters 52 a are transmitted to and decoded atcorresponding optical decoding receivers 54 a which are positioned at asafe distance from the enclosure 66. Using optical transmission provideselectrical isolation between the circuit being tested and the partialdischarge measuring instruments 56 as well as personnel. Thus, it is notnecessary for anyone to touch any of the electrical signal leads or anyother electrical connections while the circuit is undergoing testing.When tests have to be made at several accessory positions during asingle period of energization of the circuit being tested, it is onlynecessary to connect optical fiber leads 60 a from the optical encodingtransmitters 52 a to the optical decoding receivers 54 a. The opticalencoding receivers 54 a as well as the partial discharge measuringinstruments may be housed and transported in a vehicle 70 which might beequipped with a generator to provide power.

In FIG. 8, a concrete barricade 72 surrounds the buried enclosure 66 andis positioned on an earthened surface. The concrete barricade 72provides protection to personnel testing the circuit and equipment. Theconcrete barricade 72 may be covered by a heavy sheet material 74 suchas a tarpaulin to prevent rain, birds or other foreign objects fromentering the enclosure 66. Thus, with reference to FIGS. 7 and 8,partial discharge on a plurality of energized power cables is detected.Each energized power cable is interconnected by the accessory which hasthe first accessory component and the second accessory componentreleasably connectable to each other. Although not by way of limitation,the plurality of energized power cables are disposed apart from oneanother in a juxtaposed relationship and are positioned in the enclosurethat is defined by an arrangement of the walls. Electrically insulativebarriers, a plurality of electrically insulative connectors and aplurality of test links are provided.

Respective ones of the first and second accessory components aredirectly electrically connected to each other using respective ones of aplurality of test links. In this manner, direct electrical communicationis provided between the respective ones of the connected first andsecond accessory components. The electrically insulative barriers arepositioned between juxtaposed ones of the plurality of energized powercables. The electrically insulative barriers are also placed between theenergized power cables and the walls of the enclosure to further inhibitflashover. Such positioning of the electrically insulative barriersinhibits flashover. Partial discharge of the plurality of energizedpower cables is detected at the respective test links. As discussedabove, partial discharge detection is achieved by generating partialdischarge electrical signals representative of the detected partialdischarge of the respective energized power cables. The partialdischarge electrical signals are converted adjacent the enclosure toalternative energy signals that are representative of the partialdischarge electrical signals. The alternative energy signals are thentransmitted to a location remote from the enclosure. At the remotelocation, the alternative energy signals are interpreted by instrumentsto measure the partial discharge of the respective energized powercables.

The partial discharge detection test links may be left permanently inposition to allow continuous or intermittent monitoring of the energizedpower cable for partial discharge while in service. Alternatively, thepartial discharge detection test links may be removed after testing andreplaced with the conventional service links.

A method of the invention for detecting partial discharge on anenergized power cable is introduced in FIG. 9. The energized power cablehas an accessory that is interposed therein. The accessory includes afirst accessory component and a second accessory component that arecoupled to each other and are connected by a service link. In FIG. 9,step S1 provides a test link. Step S2 removes the service link. Step S3replaces the service link with the test link by directly electricallyconnecting the first accessory component and the second accessorycomponent together using the test link. Thus, electrical communicationis provided between the first and second accessory components throughthe test link. Step S4 detects the partial discharge of the energizedpower cable at the test link by generating partial discharge electricalsignals representative of the detected partial discharge. Step S5interprets the partial discharge electrical signals in a manner tomeasure the partial discharge of the energized power cable. Anadditional step might be detecting power frequency current of theenergized power cable at the test link as frequency current signals.Additionally, another step might be synchronizing the measured partialdischarge of the energized power cable with voltage frequency andvoltage phase of voltage in the energized power cable determined fromthe step of detecting power frequency current of the energized powercable.

Although the embodiments of the invention have been specificallydescribed herein, it would be apparent to those skilled in the art towhich the invention pertains that other variations and modifications ofthe embodiments herein may be made without departing from the spirit andscope of the invention.

1. A partial discharge detection test link for detecting partialdischarge of a power cable at a power cable accessory including a firstaccessory component and a second accessory component connected to eachother, the partial discharge detection test link comprising: a conductormember including an electrically conductive element and an insulationsurrounding and extending along the electrically conductive element, theelectrically conductive element having a pair of opposite ends with arespective one of ends adapted for electrical connection to a respectiveone of the first and second accessory components; and a partialdischarge sensor disposed about the conductor member, the partialdischarge sensor having a primary winding in a form of the electricallyconductive element and a secondary winding with the insulationpositioned between the primary winding and the secondary winding.
 2. Apartial discharge detection test link according to claim 1, furthercomprising an electrically conductive cable lead operably connected toand extending from the partial discharge sensor.
 3. A partial dischargedetection test link according to claim 1, wherein at least one endprojects from the insulation.
 4. A partial discharge detection test linkaccording to claim 3, wherein at least one end includes an electricallyconductive connector.
 5. A partial discharge detection test linkaccording to claim 1, wherein the electrically conductive element isfabricated from a flexible cable material.
 6. A partial dischargedetection test link according to claim 1, wherein the electricallyconductive element is a bonding lead.
 7. A partial discharge detectiontest link according to claim 1, wherein the partial discharge sensor isa radio frequency current transformer.
 8. A partial discharge detectiontest link according to claim 7, wherein the radio frequency currenttransformer is one of a ferrite-cored construction, an air-coredconstruction and a rogowski-coil construction.
 9. A partial dischargedetection test link according to claim 7, wherein the radio frequencycurrent transformer is an isolation type.
 10. A partial dischargedetection test link according to claim 7, wherein the radio frequencycurrent transformer is operative to sense electromagnetic pulsesemanating at a rapid rate from the power cable while the conductormember tolerates substantial power frequency currents flowing throughthe electrically conductive element.
 11. A partial discharge detectiontest link according to claim 10, wherein the radio frequency currenttransformer is optimized to yield high sensitivity to theelectromagnetic pulses emanating at the rapid rate.
 12. A partialdischarge detection test link according to claim 1, wherein thesecondary winding is electrically isolated from the electricallyconductive element.
 13. A partial discharge detection test linkaccording to claim 1, wherein the partial discharge sensor is connectedto the conductor member.
 14. A partial discharge detection test linkaccording to claim 1, further comprising a current transformer disposedabout the conductor member and operative to sense power frequencyflowing in the conductor member.
 15. A partial discharge detection testlink according to claim 14, wherein the current transformer is connectedto the conductor member.
 16. A partial discharge detection test linkaccording to claim 1, wherein the conductor member is connected directlyacross the accessory.
 17. A partial discharge detection test linkaccording to claim 1, wherein the insulation has a thickness and theelectrically conductive element has a diameter whereby the thickness ofthe insulation is at least one half of the diameter of the electricallyconductive element.
 18. A partial discharge detection test linkaccording to claim 1, wherein the power cable accessory is one of acable termination and a pair of bonding lead clamps.
 19. A partialdischarge detection test link according to claim 1, further comprising aground cable electrically connected to the electrically conductiveelement.
 20. A partial discharge detection test link according to claim1, further comprising an electrically insulative connector element sizedand adapted to connect the first accessory component and the secondaccessory component together while electrically insulating the firstaccessory component and the second accessory component from one another.21. A partial discharge detection system for detecting partial dischargeof a power cable at a power cable accessory including a first accessorycomponent and a second accessory component connected to each other, thepartial discharge detection system comprising: a conductor memberincluding an electrically conductive element and an insulationsurrounding and extending along the electrically conductive element, theelectrically conductive element having a pair of opposite ends with arespective one of ends adapted for electrical connection to a respectiveone of the first and second accessory components; a partial dischargesensor disposed about the conductor member and operative to detect thepartial discharge of the power cable as partial discharge electricalsignals; a first converter device electrically connected to the partialdischarge sensor and operative for receiving the partial dischargeelectrical signals from the partial discharge sensor and converting thepartial discharge electrical signals to alternative energy signalsrepresentative of the partial discharge electrical signals; a secondconverter device in communication with the first converter device andoperative for receiving the alternative energy signals and convertingthe alternative energy signals to electrical output signalsrepresentative of the alternative energy signals; and a partialdischarge measuring instrument coupled to the second converter deviceand operative to read the electrical output signals and measure thepartial discharge from the power cable.
 22. A partial dischargedetection system according to claim 21, wherein the alternative energysignals are one of optical signals and radio frequency signals.
 23. Apartial discharge detection system according to claim 22, wherein whenthe alternative energy signals are optical signals, the first converterdevice is an optical encoding transmitter and the second converterdevice is an optical decoding receiver and when the alternative energysignals are radio frequency signals, the first converter device is aradio frequency transmitter and the second converter device is a radiofrequency receiver.
 24. A partial discharge detection system accordingto claim 21, further comprising a current transformer disposed about theconductor member and operative to sense power frequency current flowingin the conductor member.
 25. A partial discharge detection systemaccording to claim 24, wherein the current transformer generates a powerfrequency current signal used in conjunction with the partial dischargemeasuring instrument for synchronizing the partial discharge measuringinstrument with voltage frequency and voltage phase of voltage in thepower cable when energized.
 26. A partial discharge detection systemaccording to claim 21, further comprising an electrically insulativeconnector element sized and adapted to connect the first accessorycomponent and the second accessory component together while electricallyinsulating the first accessory component and the second accessorycomponent from one another.